A variety of different products are used by consumers for storing, heating and for serving food for human consumption. Containers are used for cooking, storing and refrigerating, and for serving food. Each material offers certain advantages and disadvantages, depending on the application. For example, plastic food containers provide superior sealing for storing and preserving food in, for example, a refrigerator because plastic is suitable for refrigeration and can be easily molded with tongue-in-groove sealing elements for sealably coupling a lid to a container, such as in Tupperware®. Although some plastics are safe for washing in dishwashers, some are damaged by exposure to heat. Plastics may stain from exposure to certain foods, especially when foods are heated while in the plastic container. Also, plastics are generally disfavored for use as serving containers for the dining table due to a very casual appearance and feel. Recently, consumer concerns regarding the presence of Bisphenol A (“BPA”) used in hard plastics, and with the environmental impact of plastics, cause plastics to be less favored for food containers.
Metal containers, such as pots and pans, offer superior flame resistance and can be used to heat food on a stove top or in a conventional oven. Metals are dishwasher safe and are highly resistant to thermal shock. However, like plastics, metals are generally disfavored for use as serving containers for the dining table because of their metallic appearance. Metal containers are excellent conductors of heat, and a metal serving container acts as an unwanted radiator that rapidly cools the food served from the container at the table. Also, metals are highly incompatible with microwave ovens. Additionally, due to their tendency to rust or to react with other elements, metals may impart an undesirable taste to some foods. This same reactivity means that metals offer generally poor resistance to staining when brought into contact with certain foods.
Glass is another material that offers resistance to staining and is dishwasher safe. Some glass materials, such as Pyrex®, may also be used in conventional ovens and in microwave ovens. However, glass may shatter if subjected to temperature extremes, and glass is generally disfavored for use as serving containers for the dining table.
Fired ceramics are particularly favorable materials for use with foods because fired ceramics are generally microwave compatible, dishwasher safe, and highly stain resistant. Ceramics are particularly favored for use on dining tables because they can be painted and coated prior to being fired, and surface coatings imparted to ceramics are very attractive for use on the dining table, and are both washable and chip-resistant. Additionally, ceramics are generally poor conductors of heat, making them ideal for use as serving containers on a dining table. These characteristics make ceramic almost ideal for multi-purpose use; that is, fired ceramics can be used to store, heat and serve food, thereby eliminating the necessity for multiple containers for a single food. However, the problem with ceramics is that they do not provide for effective sealing to preserve the flavor and moisture in foods stored in the refrigerator or heated in the microwave.
A problem that is encountered in the use of fired ceramic containers relates to shrinkage. Articles made of fired ceramic materials are generally made from a clay material that can be shaped to form, for example, a container or a lid. In order to impart rigidity and strength to the material, it is fired in an oven for an amount of time needed to set the material. In the course of firing the ceramic material, the container or lid non-uniformly shrinks approximately 11 to 14%, and physical and dimensional irregularities commonly result from the shrinkage caused by firing. For example, a container may be fashioned from clay, and the container may be almost perfectly round. But when the container is fired in an oven, the size of the container is non-uniformly reduced, and the resulting fired ceramic container will not be perfectly round, and/or the cooled and hardened fired ceramic container may have undulations, deviations or imperfections. These imperfections may also be present in a fired ceramic lid that is made for the fired ceramic container. While these imperfections are thought by many to add an aesthetic quality to the resulting product, the non-uniform shrinkage makes it difficult to achieve a uniform clearance between mating surfaces, such as the engaging surface of the lid and the engaging surface of the container. For this reason, effective sealing is very difficult to achieve with fired ceramics.
What is needed is a ceramic container system for sealably storing foods so that the same container system can be used for storing, heating and serving food. Preferably, a container, a lid and a seal will all be microwavable and dishwasher safe. Preferably, the seal can be adapted to release pressure from the container system that may result from heating of foods within the container in, for example, a conventional oven or a microwave oven. Additionally, the container system should allow ambient air to enter the container system to prevent unwanted vapor lock. The seal should also be compatible with non-uniform mating surfaces commonly encountered in cookware fashioned from ceramic materials.